1. Field of Invention
The invention relates to an automatic transmission in which an input shaft and a mechanical reduction gear that decelerates rotation of the input shaft are connected to and capable of engaging/disengaging with each element of a compound planetary gear.
2. Description of Related Art
In Japanese Patent Laid-Open Publication No. 4-219553 (refer to FIG. 13 and paragraphs [0070] and [0071]), an automatic transmission that achieves gear ratios for six forward speeds and one reverse speed is provided. The automatic transmission includes a single pinion planetary gear that is used for deceleration and includes a ring gear connected to an input shaft, a sun gear fixed to a transmission case, and a carrier that rotatably supports a pinion meshed with the ring gear and sun gear. The automatic transmission also includes a compound planetary gear for shifting and includes first and second sun gears, combined first and second carriers that rotatably support a long pinion meshed with the first sun gear and an intermediate pinion meshed with the long pinion and the second sun gear, and combined first and second ring gears that mesh with the long pinion.
The first and second ring gears which are combined to the compound planetary gear for shifting are constantly connected to an output shaft. The rotation of a carrier of the single pinion planetary gear that is used for deceleration, the rotational speed of the input shaft thus being reduced, is selectively transmitted to the first and second sun gears of the planetary gear for shifting by a first and third clutches. The rotation of the input shaft is selectively transmitted to the combined first and second carriers of the compound planetary gear for shifting by a second clutch. Moreover, the first sun gear of the compound planetary gear that is used for shifting and the combined first and second carriers are selectively stopped from rotating by first and second brakes.